1. Field of the Art
The present invention relates to catalyst components useful for the polymerization of olefins. More specifically, the present invention relates to catalyst components for the polymerization of olefins, comprising an organoaluminum compound component having a specific structure. Further, the present invention relates to catalysts for the polymerization of .alpha.-olefins, comprising an organoaluminum compound component having a specific structure and a transition-metal compound having at least one conjugated 5-membered cyclic ligand where the transition metal belongs to one of the groups IVB to VIB in the Periodic Table; and to a method for preparing .alpha.-olefin polymers, comprising the step of bringing an .alpha.-olefin into contact with the catalyst to polymerize the .alpha.-olefin.
2. Related Art
A method for preparing .alpha.-olefin polymers in which alumoxane and a transition-metal compound are used in combination is well known (Japanese Laid-Open Patent Publications Nos. 45205/1983, 19309/1983, 35007/1985, 130314/1986, 230802/1987, 142004/1988, 234009/1988, 51408/1989 and 66214/1989). However, judging from an industrial point of view, the above technique seems to have some problems, because the activity per aluminum atom may be low, so that the production cost may be high, and a large amount of aluminum may remain in the olefin polymers produced.
Various proposals have been made in order to solve the above problems (Japanese Laid-Open Patent Publications Nos. 211307/1986, 130601/1988, 16803/1989, 22308/1990 and 167307/1990). By these proposals, the activity per aluminum atom has been improved to some extent. However, since the alumoxanes used in these proposals may have poor solubility, they may be inconvenient in handling. In addition, it may be difficult to remove aluminum from the olefin polymers produced, resulting in deterioration of the quality and the hue of the polymers. It is therefore considered that these proposals may still require further improvement.
Another proposal provides a method in which methylalumoxane is used together with another organoaluminum compound (Japanese Laid-Open Patent publications Nos. 260602/1985, 130604/1985, 89506/1988, 178108/1988, 218707/1988, 9206/1989, 315407/1989, 22306/1990 and 167310/1990). The amount of alumoxane to be used may be decreased by this proposal. However, the activity per aluminum atom would still be insufficient, so that further improvement may be required.
On the other hand, a catalyst component for the polymerization of olefins, comprising an alumoxane compound having two or more types of alkyl groups has been proposed as a new attempt (Japanese Laid-Open Patent Publications Nos. 247201/1990, 250886/1990, 46906/1992, 26410/1992 and 266910/1992). Further, there is also a proposal in which an alumoxane compound obtained by substituting a part of the alkyl groups contained in the above alumoxane compound with hydrogen is employed (Japanese Laid-Open Patent Publication No. 139503/1991). However, all of these alumoxane compounds have a high association degree, so that it may be necessary to use a large amount of the alumoxane compounds in order to maintain high activity. Moreover, they are soluble only in an aromatic solvent, so that they would have many industrial restrictions.
The use of a tetraalkylalumoxane compound has been proposed so as to obtain polymers having lowered molecular weight (Japanese Laid-Open Patent Publication No. 197514/1991). This alumoxane compound is advantageous in that it is readily soluble also in an aliphatic hydrocarbon solvent. However, although this alumoxane compound reveals high activity when used for the polymerization of ethylene, it may exhibit extremely low activity when used for the polymerization of .alpha.-olefins such as propylene. Therefore, this proposal may also require further improvement.
Reaction products of an organoaluminum compound and an oxygen-supplying compound other than water (for instance, boroxine or alkyltin oxide) have been proposed (Japanese Laid-Open Patent Publications Nos. 256686/1990, 304202/1992, 304203/1992 and 304206/1992). However, the products obtainable by any of the methods described in these publications are alumoxanes having an Al--O--Al bond, so that they seem to have the same problems as the above.
On the other hand, reaction products of a dihydric alcohol or a primary amine and an organoaluminum compound have been proposed as organoaluminum compounds other than alumoxane compounds (Japanese Laid-Open Patent Publication No. 62806/1991). However, the organoaluminum compounds obtained by this reaction can exhibit, in general, only extremely low polymerization activity when they are used in combination with a metallocene compound. For this reason, these compounds are unsatisfactory as substitutes of alumoxane compounds, and require further improvement.
An object of the present invention is to solve the various problems accompanying the above-described prior art. Another object of the present invention is to provide a cocatalytic component useful for producing polymers having high molecular weight.